diff --git a/backend/python/fish-speech/install.sh b/backend/python/fish-speech/install.sh
index 6e1ab8c95e91..4be2cd2d294e 100644
--- a/backend/python/fish-speech/install.sh
+++ b/backend/python/fish-speech/install.sh
@@ -13,6 +13,17 @@ fi
 # fish-speech uses pyrootutils which requires a .project-root marker
 touch "${backend_dir}/.project-root"
 
+# On darwin arm64 the transitive `tokenizers` dep compiles its Rust extension
+# from source (Linux uses prebuilt manylinux wheels, so it never compiles
+# there). The pinned tokenizers crate that fish-speech's stack resolves to
+# contains a `&T` -> `&mut T` cast that trips the now-deny-by-default
+# `invalid_reference_casting` lint in the macOS runner's newer Rust toolchain,
+# breaking the build (seen in the v4.5.5 release CI fish-speech darwin/metal
+# job). Allow that lint so the unchanged third-party crate compiles as before.
+# Append rather than clobber any pre-existing RUSTFLAGS; harmless on Linux
+# where no Rust compile happens.
+export RUSTFLAGS="${RUSTFLAGS:-} -A invalid_reference_casting"
+
 installRequirements
 
 # Clone fish-speech source (the pip package doesn't include inference modules)